The red imported fire ant (Solenopsis invicta) is an injurious insect giving great damages to agricultural products such as soybean, etc., through middle South America to the southern and middle part of the United States of America. A method of using chlorine series agricultural chemicals such as dieldrin, etc., had conventionally been used as a method of controlling the red imported fire ant (Solenopsis invicta), but from the problems of a chronic toxicity, an in-soil remaining property, etc., the use of the chlorine series agricultural chemicals have been entirely prohibited.
With the prohibition of using the agricultural chemicals, various controlling methods have been investigated and, in particular, a method of using a pheromone and an anticidal agent has recently been noticed in the United States of America [Tetrahedron, 43(13), 2897-2900(1987), and J. Chem. Ecol., 14(3), 825-838(1988)].
Further, of the pheromones of the red imported fire ant (Solenopsis invicta), the queen recognition pheromone is a pheromone with which working ants recognize the queen ant and it is reported that ants can be effectively controlled by utilizing the queen recognition pheromone.
Three kinds of components represented by the following formulae (I), (II), and (III) are known as the queen recognition pheromone of the red imported fire ant (Solenopsis invicta). Of those components, (-)-3,5-dimethyl-6-(1'-methylbutyl)-2H-tetrahydropyran-2-one represented by the formula (II) called invictolide has 4 asymmetric carbon atoms in the structural molecule, and the synthesis of the compound is very difficult. ##STR1##
A stereoselective synthesis method of (-)-3,5-dimethyl-6-(1'-methylbutyl)-2H-tetrahydropyran-2-one (invictolide) described above is shown in the report by Ziegler et al [Tetrahedron Letters, 27, 1229(1989)]. However, this method has the problems that the method includes very many reaction steps, and the optical purity of invictolide obtained is low, and hence this method is not a production method which can be widely used in an industrial purpose.
Under such circumstances, a synthesis technique capable of easily conducting the synthesis of invictolide is disclosed in U.S. Pat. No. 4,864,056.
The disclosed technique is a technique of synthesizing invictolide which is one component of the queen recognition pheromone, using an optically active hydroxy ester represented by the following formula (IV), and this technique can synthesize invictolide represented by the formula (II) at a high purity and with short steps as compared with the above-described method reported by Ziegler et al. ##STR2##
However, the stereoselective synthesis method of invictolide using the hydroxy ester disclosed in U.S. Pat. No. 4,864,056 described above involves the problems that 13 reaction steps described hereinafter must be passed from the synthesis of the optically active hydroxy ester to the synthesis of invictolide and hence the synthesis method is not a sufficient technique as a synthesis method which is widely used as an industrial method.
The synthesis steps shown in the techniques already disclosed are explained by the reaction schemes 1 to 3 shown below.
First, an optically active epoxide (b) is synthesized from an optically active amino acid (a) as shown in following reaction scheme 1. ##STR3##
Next, the epoxide (b) is subjected to a ring-opening reaction and an acid treatment according to the following reaction scheme 2 to obtain a hydroxylic acid (c) and the hydroxylic acid (c) is methyl-esterified to obtain a hydroxy ester (d). Furthermore, the hydroxy ester (d) is reacted with lithium diisopropylamide and methyl iodide in the presence of a base to .alpha.-methylate the ester and is then through a separation and purification step to synthesize an optically active hydroxy ester (e). ##STR4##
Using the optically active hydroxy ester (e) thus synthesized, invictolide (k) is synthesized according to the reaction scheme 3 shown below.
First, the optically active hydroxy ester (e) is reacted with dihydropyran in the presence of an acid catalyst to synthesize a compound (f) the hydroxy group of which is protected, and the product obtained is then reduced with aluminum lithium hydride to obtain a compound (g). The compound (g) is tosylated to obtain a compound (h), the compound (h) is iodinated to synthesize a compound (i), and the compound (i) is then asymmetrically alkylated to obtain a compound (j). The compound (j) is subjected to an acid treatment to obtain the invictolide (k). ##STR5##
As described above, many reaction steps are also required in the synthesis technique already disclosed and hence the synthesis technique is not a sufficient technique which is widely used as an industrial synthesis method.
Thus, the development of an excellent synthesis method capable of synthesizing invictolide, which is a component of the gueen recognition pheromone, at a high optical purity and easily in less reaction steps and capable of establishing as an industrial production method has been desired in the field of the art.